Introduction

In 1939, Louis Hamman described spontaneous pneumomediastinum, also known as Hamman’s syndrome [1], defined as presence of free air within the mediastinum not caused by trauma, surgical, or medical procedure (including mechanical ventilation). Charles Macklin proposed its pathologic mechanism, consisting in an alveolar rupture secondary to a lung over-inflation, with subsequent air dissection along the bronchoalveolar sheath (interstitial emphysema), reaching the pulmonary hilum, then the mediastinum and then other anatomical regions, such as submandibular space, retropharyngeal space, large neck vessels, and esophagus. It can also spread to the peritoneal cavity through aortic and esophageal spaces [2].

Spontaneous pneumomediastinum is a rare disease, with incidence of one in 24,945 to one in 40,000 patients admitted to the emergency service [3, 4]. Children present a bimodal peak incidence, in younger than 7 years old and from 15 − 18 years old groups [5, 6]. It is a rare and self-limiting condition in children that can cause widespread subcutaneous emphysema. We present two cases of exacerbated asthma complicated with spontaneous subcutaneous emphysema and pneumomediastinum as part of an air leak syndrome.

Case presentation

Case 1

A 2-year-old girl consulted our pediatric emergency department with 4 days of fever, cough, nasal congestion, rhinorrhea, and ocular discharge. She had a history of bronchiolitis at 8 months of age and four more wheezing episodes thereafter. Her vital signs on admission were blood pressure 100/60 mmHg, heart rate 147 per minute, respiratory rate 44 per minute, oxygen saturation (SpO2) at 80% on room air, and temperature of 38.7 °C. She had suprasternal and subcostal retractions and on pulmonary auscultation, inspiratory, and expiratory wheezing. Her initial laboratories tests showed: 18,200/mm3 leukocytes, 11,500/mm3 neutrophils, 12.4 g/dL hemoglobin, 596,000/mm3 platelets, and a 20.4 mg/L C-reactive protein (normal value: < 5 mg/L). Chest x-rays showed lung hyperinflation, interstitial opacities, and subsegmental atelectasis. She was initially treated with a beta-2 agonist (salbutamol), oxygen therapy by cannula, and one dose of dexamethasone. At reassessment, 2 h after admission, she had subcostal, intercostal and supraclavicular retractions, and nasal flaring so intravenous methylprednisolone and inhaled beclomethasone were added.

At 48 h after admission, her respiratory distress worsened, with a SpO2 of 74% with a-2 l/min cannula and irritability that resolved with analgesia. At that time, it was noted that she had subcutaneous emphysema in her chest and neck. Due to her respiratory distress, we initiated oxygen through a high-flow nasal cannula at 12 l/min with a FiO2 of 0.6. New chest x-rays showed pneumomediastinum and subcutaneous emphysema, alveolar opacities in the left perihilar and right basal locations (Fig. 1a). Her new tests showed: 16,000/mm3 leukocytes, 11,680/mm3 neutrophils, 11.1 g/dL hemoglobin, 809,000/mm3 platelets, and 7.9 mg/L C-reactive protein. Suspecting a bacterial coinfection, she was started on ampicillin-sulbactam. A chest computed tomography showed a widespread subcutaneous emphysema, pneumomediastinum, and parenchymal bands in middle lobe and lingula, consolidation in posterior basal segments, with no evidence of esophageal, tracheal, or bronchial lesions (Fig. 1b and c). She did not require surgical interventions, received 3 days of high-flow nasal cannula, then continued with conventional nasal cannula, antibiotics, methylprednisolone, analgesia, and bronchodilators with a complete recovery. On the eighth day of stay, she was discharged.

Fig. 1
figure 1

a Frontal chest x-ray with subcutaneous emphysema (white arrow). Air outlines the central portion of the diaphragm under the heart, giving rise to a continuous diaphragmatic contour that extends from one lateral chest wall to the other (continuous diaphragm sign) (black arrow). b, c Chest computed tomography image shows subcutaneous emphysema (white arrow); pneumomediastinum (white arrowhead); presence of air around pulmonary vessels, suggestive of pulmonary interstitial emphysema (black arrow); air outlines the central portion of the diaphragm under the heart (black arrowhead)

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Case 2

A 16-year-old boy with a history of asthma, admitted due to dyspnea, oropharyngeal pain, and dysphagia. Vital signs on admission were blood pressure 123/58 mm Hg, heart rate 117 per minute, respiratory rate 20 per minute, temperature 36.4 °C, and SpO2 if 86% on room air. On pulmonary auscultation, he had inspiratory and expiratory wheezing. He was treated with oxygen through a conventional nasal cannula, beta-2 agonist (salbutamol), and steroids (inhaled beclomethasone and oral prednisolone). After 36 h of admission, he referred chest pain, and on physical exam a subcutaneous emphysema of the cervical, supraclavicular, and dorsal areas was noted. Chest x-ray showed a pneumomediastinum, an image suggestive of a right pneumothorax, subcutaneous emphysema, and thickening of the bronchial walls (Fig. 2a and b). He was assessed by the surgical department, and they consider no indication for surgical procedures. On the fourth day of stay a new chest x-ray was performed, showing improvement in the subcutaneous emphysema, without pneumomediastinum. With this image and no further need of supplemental oxygen, he was discharged with a scheduled outpatient follow-up.

Fig. 2
figure 2

a Frontal chest x-ray with subcutaneous emphysema (white arrow), continuous diaphragm sign (black arrow), and pneumomediastinum (white arrowhead). We can see a lucent band of gas extending along the descending aorta and intersecting band that extends along medial left hemidiaphragm, together forming “V” (Naclerio’s V sign) (black arrowheads). Also, a lucent cap bounded by a pleural line which can be an extra pleural extension of gas from pneumomediastinum or a pneumothorax (white arrowhead with black borders). b Lateral chest x-ray with pneumomediastinum outlining thorax structures and shows a broad band of gas separating anterior pericardium from sternum (white arrows). Lucent ring around extra pericardial segment of right pulmonary artery, ring-around-the-artery sign (white arrowheads). Gas outlines the superior surface of left hemidiaphragm, which is normally obscured by heart (continuous left hemidiaphragm sign) (black arrowheads)

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Discussion

We present two pediatric patients with an air leak syndrome secondary to bronchial obstruction. In both patients, we managed the underlying disease, with control of the infection and asthma exacerbation, without requiring surgical interventions. Additional studies like chest-computed tomography and follow-up chest x-rays did not change our management. These cases demonstrate how air leak syndromes can be managed conservatively, and additional studies may not be required.

Spontaneous pneumomediastinum is a rare disease in children, more prevalent in boys (67–87%) [3,4,5, 7, 8]. It occurs in bimodal peaks in children younger than 7 years old and then in 15 − 18 years old [5, 6]. Predisposing factors for the development of these leaks are infections (12–43%), asthma (11–24%), physical exertions (14–24%), or some are idiopathic (35%) [3, 5, 8].

Pediatric patients may consult with dyspnea (36–65%), chest pain (48–89%), cough (41%), neck pain or sore throat (33–57%), dysphagia (8–40%), or back pain (11–19%). Physical findings are subcutaneous emphysema (60–87%), extending to the neck (40%), Hamman’s sign (16–53%), wheezing (22%), torticollis (11%), or no apparent signs (8–22%) [3,4,5, 7, 8]. The presence of subcutaneous emphysema in the neck or supraclavicular tissue is the most useful predictor of an air leak [6].

Pneumomediastinum manifests radiologically by lucent streaks or gas bubbles outlining mediastinal structures. Gas is most often visible just above the heart on the left. In a lateral chest x-ray, gas causes lucent streaks outlining the ascending aorta, aortic arch and its branches, pulmonary arteries, trachea, and proximal bronchi. Other pneumomediastinum signs described are a continuous diaphragm sign, continuous left hemidiaphragm sign, Naclerio’s V sign, the ring-around-the-artery sign, extrapleural air sign [9]. A chest radiograph confirms pneumomediastinum in all patients as described previously [3, 7]. Radiological follow-up is not necessary, but up to 55% of patients with radiological follow-up showed improvement in or complete resolution of mediastinal air usually within 24 h [6]. Imaging studies beyond the initial chest x-rays (including computed tomography scans), do not lead to changes in treatment [8]; just as it was observed in our first case.

Up to 12–35% of children have concomitant pneumomediastinum, pneumothorax, and dyspnea [3,4,5] and patients with asthma have a higher risk of developing concomitant pneumothorax. Mediastinal pleura stretching can lead to rupture and pneumothorax [2]. Pneumothorax diagnosis in pneumomediastinum must be done carefully, since an apical extension of pneumomediastinum can create a lucent cap bounded by a pleural line. However, there are important differences. Pneumothorax is usually mobile within the pleural space, whereas extra pleural gas is confined within tissue planes. Also, in apical extension of pneumomediastinum, the pleural line may not form a smooth arc as it does in pneumothorax, secondary to tethering by overlying fascia. Finally, apical extra pleural gas is almost always bilateral and is always accompanied by clear evidence of pneumomediastinum extending toward the neck, while pneumothorax is usually unilateral and is not accompanied by pneumomediastinum [9].

These air leaks are often benign conditions with short length of hospital stay ranging from 1–10 days [3, 5, 7, 8]. Up to 20–46% of children, especially with young age and acute infections may present respiratory distress and require intensive care [3, 5, 8]. Admission to the intensive care unit should be based on the underlying medical problem independent of the presence of a pneumomediastinum [8]. Both our cases were successfully managed with oxygen, corticosteroids, and bronchodilators. Our first patient required antibiotics because of bacterial coinfection. Treatment consists of analgesia, rest, oxygen therapy, and management of the underlying condition [5, 7, 8]. None of the patients developed any complications, all had complete or near complete resolution of findings on chest radiography before discharge [7]. Evidence available to date states that if the child is clinically stable, the pneumomediastinum can be observed and discharged without further control x-rays and they only need to rest [9].

Our patients presented with bronchial obstruction. On long-term follow-up (6–120 month), up to 33% of patients with an abnormal pulmonary function had a spontaneous air leak as the presenting feature of a subclinical and clinical asthma [6]. The air leak syndrome related to asthma in children can be successfully treated with conservative management. This would help the pediatric generalist in managing such cases although intense monitoring may be warranted.